Optical sensor for rotational movements having an optical running period element

ABSTRACT

An optical sensor for rotational movements is proposed that includes a semiconductor laser that is at least intermittently activated, and whose frequency-modulated beam is split into two partial beams that respectively pass through an annular optical fiber arrangement in opposite directions, are subsequently superposed as coupled-out signals and conducted to a photodetector that emits an output signal that has a predeterminable heterodyne frequency, and whose phase position permits the determination of the rate of rotation of the arrangement with respect to a reference signal. The sensor of the invention can be installed into integrated optics, wherein all of the optical beams can be guided in optical fibers. The sensor of the invention is particularly suited as an optical fiber gyro or a rotation rate sensor.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention is based on an optical sensor for rotational movements ofthe generic type having a laser beam source, a device for splitting thebeam emitted by the laser beam source into first and second partialbeams, an annular optical fiber arrangement into which the first partialbeam is coupled in a first direction and the second partial beam iscoupled in a second direction, with the first and second directionsbeing opposite, and a photodetector into which first and second partialbeams are coupled out of the annular optical fiber arrangement aresupplied. An optical sensor of this type is known from the publicationby K. HOTATE and S SAMUKAWA, "Drift reduction in an optical heterodynefiber gyro," Applied Optics, Vol. 29, No. 9, Mar. 20, 1990, pp.1345-1349. The Sagnac effect, which occurs in a fiber optical gyro, isthe basis of the known sensor. The beam generated by a laser diode issplit into two partial beams with a grating and a beam splitter, andsubsequently coupled into an optical fiber disposed in annular form. Onepartial beam passes through the fiber clockwise, and the other partialbeam passes through counterclockwise. The beams coupled out of the fiberare conducted through the beam splitter and impact upon anacousto-optical modulator that superposes the beams. The grating and theacousto-optical modulator, whose angles of diffraction are identical,are disposed symmetrically with respect to the beam splitter. Aphotodetector receives a non-refracted portion of the beam that hascirculated clockwise in the fiber, the frequency of the beam beingidentical to the frequency of the semiconductor laser beam. Moreover,the photodetector receives a diffracted portion of the beam rotatingcounterclockwise in the fiber and having a frequency that is altered bythe magnitude of the frequency generated by the acousto-opticalmodulator, with respect to the beam produced by the semiconductor laser.The photodetector emits as an output signal the altered frequencydesignated as the heterodyne frequency. A rotation of the optical fiberresults in a phase shift between the signal emitted by the photodetectorand the signal that controls the acousto-optical modulator.

The authors of the publication concede that this above-described opticalsensor for rotational movements has drawbacks with regard to zero-pointstability that are particularly a function of a temperature drift of theacousto-optical modulator. Thus, in one feature of the known device, areference path is incorporated that represents an optical short-circuitwith respect to the annularly-disposed optical fiber, and upon which themeasuring effect has no effect. The measurement process is subdividedinto two time segments. The phase of the output signal of thephotodetector is stored during the first segment, which must be shorterthan the running period of the optical beam through theannularly-disposed acousto-optical modulator, and the two partial beamspass through the optical short-circuit path practically without a timedelay. During the second segment, the partial beams coupled out of theannular optical fiber, which at this point have already passed throughthis fiber, are received by the photodetector. The measurement result isdetermined through comparison of the phase position of the photodetectorsignal obtained in the second segment with the photodetector signalobtained in the first segment.

The object of the invention is to provide an optical sensor forrotational movements that can be realized with simple means.

SUMMARY OF THE INVENTION

In accordance with a first embodiment of the sensor of the device, afirst beam coupler is provided for coupling out a second partial beamthat has passed through an annular optical fiber and for guiding a firstpartial beam to be coupled into the fiber, and a second coupler isprovided for coupling out the first partial beam that has passed throughthe annular optical fiber and for guiding the second partial beam to becoupled into the fiber. The coupled-out partial beams are superposed andsupplied to the photodetector. A signal that can be emitted by thephotodetector and that is simple to evaluate is obtained when the twocoupled-out beams have a frequency difference that leads to a differencefrequency during superposition of the two coupled-out beams that iswithin, for example, the kHz or MHz range. The frequency difference isachieved by means of a modulation of the frequency of the laser beamsource and the use of an optical running period element in one of thetwo partial beams. A phase comparator determines the phase differencebetween a signal that corresponds to the laser beam source and thesignal emitted by the photodetector. The rate of rotation of the entiresensor can be determined from the phase difference.

The essential advantage of the sensor of the invention lies in itssimple design, which only requires conventional fiber optical elements.Because of this, the entire sensor can be designed to be very small andcost-effective. In addition, the option of guiding the occurring opticalbeams only in optical fibers is particularly advantageous. Interferinginfluences that could act on externally propagating beams can be avoidedwith this measure.

The described advantages apply equally for the further embodiments ofthe sensor in accordance with the invention.

The optical sensor of the invention for rotational movements is suitedas an optical fiber gyro in various applications. It is particularlysuited as a rotational rate sensor that is provided in, for example, amotor vehicle to control the drive hydraulics. The possible constructionwith components of the integrated optics, and a compact design withoutmechanically moved components, make the optical sensor of the inventionparticularly suitable for installation in vehicles of all types that canbe subjected at times to harsh environmental conditions.

In a second embodiment of the sensor in accordance with the invention, abeam path is provided between the first and second couplers thatsupplies the first partial beam to the photodetector via the secondcoupler and the second partial beam to the photodetector via the firstcoupler. This beam path corresponds to the reference path described atthe outset in the prior art. However, the further construction and beamguidance are vastly different. Also in this embodiment, a modulator formodulating the beam frequency of the laser and the optical runningperiod element are provided in one of the two partial beams. In additionto the frequency modulation, a further operating mode of the laser isprovided, in which the laser is activated for a first, predeterminabletime and deactivated for a second, predeterminable time. A providedphase comparator determines a phase difference between the signalemitted by the photodetector during the first time and the signalemitted by the photodetector during the second time.

The advantage of this embodiment in contrast to the first embodiment isthat only the signals emitted by the photodetector are used to determinethe phase difference. Interfering influences that affect the opticalpaths do not influence the result.

In accordance with a third embodiment of the sensor of the invention, itis provided that a portion of the first partial beam is coupled out ofthe first coupler as the first reference beam, and a portion of thesecond partial beam is coupled out of the second coupler as a secondreference beam. The two reference beams are conducted to a referencephotodetector. A phase comparator is provided that determines a phasedifference between the signals emitted by the photodetector and thereference photodetector.

The advantage of this embodiment is that signals whose phase differencecan be determined by the phase comparator can be continuously detectedat the two photodetectors. Intermittent laser operation is omitted.

Advantageous features and improvements of the optical sensor forrotational movements in accordance with the invention ensue from thefollowing description.

The embodiment of the entire optical design is advantageously in opticalfiber technology. A disturbance of the different beams by environmentalconditions is therefore prevented to a great extent. Furthermore, withthis measure the structural design of the sensor can be selectedarbitrarily within a large scope.

The use of a third beam coupler to unite the two coupled-out partialbeams is advantageous. The adjustment procedure that would be necessarybecause of the superposition of the two partial beams directly at thephotodetector is thus eliminated. For the same reasons, the use of afourth coupler in the third embodiment to superpose the two referencebeams is advantageous.

Presetting the same times in the second embodiment during which thelaser is activated and deactivated results in the highest possiblemeasured rate.

Additional advantageous features and improvements of the optical sensorfor rotational movements in accordance with the invention ensue from thefollowing description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an embodiment of an optical sensor for rotational movementin accordance with the invention, FIGS. 2 and 3 show functionalrelationships of frequencies of optical beams as a function of the time,FIG. 4 shows a different embodiment of an optical sensor for rotationalmovements in accordance with the invention, FIG. 5 shows in its upperpart a functional connection between an activated period and a pause ofa laser and, in its lower part, a functional relationship betweenfrequencies of optical beams and the time, and FIG. 6 shows a furtherembodiment of an optical sensor for rotational movements in accordancewith the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a laser beams source 10, which transmits a beam 11 to means12 for splitting the beam 11 into a first and a second partial beam 13,14.

After passing through an optical running period element 15, the firstpartial beam 13 enters a first coupler 16, which it exits as a firstbeam 13' to be coupled into an annular optical fiber arrangement 17.After passing through the arrangement 17, the first partial beam 13, 13'is supplied as a first beam 13" to be coupled out to a second coupler18, which it exits as a first coupled-out beam 13"'. After passingthrough a third coupler 19, the first coupled-out beam 13"' reaches aphotodetector 21 as an output beam 20.

After passing through the second coupler 18, the second partial beam 14becomes the second beam 14' to be coupled into the annular optical fiberarrangement 17. With respect to the first beam 13' to be coupled in, thesecond beam 14' to be coupled in is coupled into the arrangement 17 inthe opposite direction. The second beam 14' to be coupled in exits thearrangement after passing through as the second beam 14" to be coupledout, and travels to the first coupler 16. The first coupler 16 conductsthe second beam 14" to be coupled out to the third coupler 19 as thesecond coupled-out beam 14"', which coupler superposes the beam with thefirst coupled-out beam 13"' to become output beam 20.

The laser 10 is activated by a modulator 22 with a modulation signal 23.The modulator 22 further transmits a signal 24 that corresponds to themodulation signal 23 to a phase comparator 25, to which an output signal26 of the photodetector 21 is also supplied. A signal that represents ameasure for the rate of rotation of the sensor can be taken at an output27 of the phase comparator 25. The rotation of the sensor has as areference a mid-point, not shown in FIG. 1. The two directions ofrotation are indicated with reference numeral 28 in FIG. 1.

FIG. 2 shows a functional relationship between a frequency 30 of thebeam 11 emitted by the laser 10 and the time 31. The maximum frequencydifference 32, which is predetermined by the modulation signal 23,occurs within a time interval 33.

FIG. 3 shows a functional relationship between a frequency 40, which thefirst beam 13' to be coupled in and the second beam 14' to be coupled inhave, and the time 41. The curve course with reference numeral 42corresponds to the frequency course of the second beam 14' to be coupledin, and the curve course indicated by reference numeral 43 correspondsto the frequency course of the first beam 13' to be coupled in. Curvecourses 42, 43 are staggered with respect to one another by the timeinterval 44, and therefore have a frequency offset 45. The time interval46 shown in FIG. 3 corresponds to the interval 33 shown in FIG. 2.

The function of the optical sensor for rotational movements shown inFIG. 1 is explained in detail by means of the functional relationshipsshown in FIGS. 2 and 3:

The optical sensor for rotational movements in accordance with theinvention determines the rate of rotation of the annular optical fiberarrangement 17, and thus that of the entire sensor, in one of the twodirections of rotation 28. The absolute angular position in relation toa reference angle, as well as an angular acceleration or othercharacteristic values, can be derived from the rate of rotation. Thechange in the running period of an optical beam in arrangement 17 thatoccurs as a result of a path lengthening caused by the rotationalmovement is used. When the arrangement 17 rotates clockwise, theeffective path shortens, for example, that is, the return path of thebeam 13' to be coupled in that is in the arrangement 17, while at thesame time the path of the beam 14' to be coupled in extends. Aftersuperpositioning of the two coupled-out beams 13"', 14"', the entirebeam can alternate between the value zero and a maximum value. Theabsolute level of the output signal 26 emitted by the photodetector 21would have to be evaluated. Therefore, the heterodyne measurement methodis provided, in which the beams 13', 14', to be coupled in already havea predetermined frequency difference. With this measure it is achievedthat, even when the arrangement 17 is at rest, an output signal 26 isobtained at the photodetector 21 whose frequency corresponds to thesuperposition frequency, and only the phase difference between thisoutput signal 26 and a signal 24 that corresponds to the modulationsignal 23 is to be evaluated in the phase comparator 25 to determine therate of rotation.

The modulation signal 23 emitted by the modulator 22 modulates thefrequency of the beam 11 emitted by the laser 10. The laser 10 ispreferably a semiconductor laser whose current can be modulated. Thefrequency course of the beam 11 is shown in FIG. 2 as a function of thetime. The frequency modulation amplitude corresponds to the maximumfrequency difference 32 that occurs during the time interval 33 thatcorresponds to the modulation period. The frequency difference 32 to bepredetermined can be seen in in the relationship with the opticalrunning period element 15, which is disposed in the beam path of thefirst partial beam 13 or in the beam path of the second partial beam 14.The running period element 15 is realized, for example, as an opticalalternate route in optical fiber technology. The alternate route 15causes a frequency shift between partial beams 13, 13', 13", 13"", 14,14', 14", 14"' that is shown in FIG. 3. The time interval 44 correspondsto the running period of the optical beam in the alternate route 15. Theresulting frequency difference, which is given at all times, is shown inFIG. 3 with frequency offset 45. Interval 44 is shown with anexaggerated length in comparison to interval 33, 46. Interval 44 iswithin the nanosecond range, for example, which corresponds to analternate route 15 within the meter range. Interval 33, 46, in contrast,is within the millisecond range, for example. Frequency offset 45results from the maximum modulation frequency amplitude 32 being dividedby the time interval 33, 46 and multiplied with the running period ofthe alternate route 15. Frequency offset 45 is set within the kHz or MHzrange, for example.

A rotation of arrangement 17 leads to a change in the phase position ofoutput signal 26. The rate of rotation can be determined by comparisonof the phase of output signal 26 with the phase of a reference signal.The reference signal is derived from the modulator 22. It emits signal24, which corresponds to modulation signal 23 and has a periodcorresponding to, for example, time interval 33, 46. The signal 24corresponding to the modulation signal 23 has a fixed phase relationshipto the output signal 26 when arrangement 17 is at rest. A directcomparison of the phase position of signals 24, 26 is generally notpossible. The comparator 25 determines the difference by means of apredetermined correction factor that can be determined theoretically orthrough experiments. A signal that is a measure for the rate of rotationof the annular optical fiber arrangement 17, and thus for the rotationrate of the entire sensor, is available at the comparator output 27.

FIG. 4 shows a different embodiment of the optical sensor for rotationalmovements in accordance with the invention. In FIG. 4, those parts thatcorrespond to the parts shown in FIG. 1 have the same reference numeralsas in FIG. 1. A first essential difference in the function of the sensorshown in FIG. 4 as compared to the sensor shown in FIG. 1 is that thelaser 10 emits no continuous beam. The beam emitted by the laser 10 istherefore indicated in FIG. 4 by reference numeral 50. The beam 50 issplit into a first and second partial beam 51, 52. After passing throughalternate route 15 and the first coupler 16 as a first beam 51' to becoupled in, the first partial beam 51 enters arrangement 17. The secondpartial beam 52 becomes a second beam 52' to be coupled in after passingthrough coupler 18. The two beams 51', 52' to be coupled in travel inopposite directions in arrangement 17. After passing through arrangement17, the first beam 51' to be coupled in is conducted to the secondcoupler 18 as a first beam 51" to be coupled out. The second beam 52' islikewise conducted to the first coupler 16 as a second beam 52" to becoupled in after passing through arrangement 17.

An optical short-circuit 53 is provided between the two couplers 16, 18.The first coupler 16 couples out a part of the first partial beam 51 asa first reference beam 51"', which is supplied to the second coupler 18.The second coupler 18 couples a part out of the second partial beam 52as a second reference beam 52"', which is supplied to the first coupler16. A first beam 51"" is coupled out of the first coupler 16, and asecond beam 52"" is coupled out of the second coupler 18. Thecoupled-out beams 51"", 52"" respectively correspond in temporalsequence to the first beam 51" to be coupled out and the second beam 52"to be coupled out, as well as the first reference beam 51"' and secondreference beam 52"'. The temporal relationship will be described laterby means of the functional relationships shown in FIG. 5. The beam 50 oflaser 10 is activated and deactivated as well as modulated in itsfrequency with a modulation signal 54. Modulation signal 54 is madeavailable by a modulator 55 that transmits a further control signal 56to a phase comparator 57. The phase comparator 57 determines phaserelationships, as a function of control signal 56, between the outputsignals 58 occurring in temporal sequence that occur at thephotodetector 21.

The upper portion of FIG. 5 shows a functional relationship between anoperating time 59 and an operating pause 60 of laser 10 as a function ofthe time 61. The lower portion of FIG. 5 shows a functional relationshipbetween a frequency 62 of the beam 50 emitted by the laser 10 and thetime 61. The same temporal measures are the basis of the upper and lowerportions of FIG. 5. Shown is the maximum frequency difference 65, whosevalue can correspond to the frequency difference 32 shown in FIG. 2. Thefrequency modulation takes place during a first time interval 63, whichcorresponds to the operating time 59 of laser 10. The further course ofthe frequency change after the first time interval 63 is insignificant,because the operating pause 60 of laser 10 occurs during the successivetime interval 64. The function of the sensor shown in FIG. 4 isexplained in detail in connection with the functional relationshipsshown in FIG. 5:

The modulator 55 transmits the modulation signal 54 to the laser 10 thatactivates the laser for the operating time 59, which is followed by theoperating pause 60. During the operating time 59 the frequency of a beam50 emitted by the laser 10 is varied by means of modulation signal 54,in which instance the maximum frequency difference 65 is determined inconnection with alternate route 15 in order to obtain a predeterminedheterodyne frequency at photodetector 21. The at least nearly linearrise in frequency 62 shown in the lower portion of FIG. 5 results in aheterodyne frequency at photodetector 21 that remains constant duringthis time. In place of the linear rise, a different, arbitrarycharacteristic can also be predetermined, with which, however, theheterodyne frequency is altered temporally. In comparison to theinterval 33 shown in FIG. 2, the first time interval 63 is considerablyshorter. The first time interval 63 is advantageously determined in sucha manner that, during the first time interval 63, beams 51", 52" to becoupled out have not reached the photodetector 21 through the annularoptical fiber arrangement 17 because of their running periods. The firsttime interval 63 is within, for example, the microsecond range when alength of, for example, several hundred meters is provided for theannular optical fiber arrangement 17. However, during the first timeinterval 63, reference beams 51"', 52"' guided via the short-circuit 53already reach the photodetector 21 as coupled-out beams 51"", 52"".Coupled-out beams 51"", 52"" can be superposed either directly at thephotodetector 21 or in the third coupler 19. The signal 58 emitted byphotodetector 21 during the first time interval 63 and having theheterodyne frequency is evaluated with respect to its phase position inthe comparator. The phase position of signal 58 during the first timeinterval 63 is compared with the signal 58 emitted subsequently byphotodetector 21 during the second time interval 64. This signal is aresult of the beams 51", 52" to be coupled out, which, after passingthrough the arrangement 17, are available only as long as the first timeinterval 63 has lasted Signals 51", 52" to be coupled out are superposedin the third coupler 19 as coupled-out signals 51"", 52"" and conductedto the photodetector 21. The rate of rotation can be determined from thedetermination of the difference of the phase position of the signalemitted by the photodetector 21 during the second interval 64 and thesignal emitted during the first interval 63, and made available at theoutput 27 of the phase comparator 57. At the end of the second timeinterval 64, whose length is advantageously selected to be identical totime interval 63, the first time interval 63 follows again. With thismeasure, a maximum measuring rate without pauses is attained.

In the embodiments in FIGS. 1 and 4 of the sensor of the invention, itis possible to dispose the optical running period element 15 in one ofthe coupled-out beams 13"', 14"' (FIG. 1) or in one of the coupled-outbeams 51"", 52"" (FIG. 4). With this measure it is achieved that thebeams in the optical fiber arrangement 17 have the same frequency at alltimes. Phase disturbances that have various effects at differentfrequencies are then compensated.

FIG. 6 shows a further embodiment of the sensor for rotational movementsin accordance with the invention. Those parts that correspond to theparts shown in FIG. 1 have the same reference numerals in FIG. 6 as inFIG. 1. The sensor shown in FIG. 6 corresponds extensively in design andfunction to the sensor shown in FIG. 1. The essential difference is thata comparison signal 70, with which the output signal 26 of thephotodetector 21 is compared, is obtained from the optical arrangement.A first reference beam 13"" is coupled out of the first partial beam 13with the first coupler 16, and a second reference beam 14"" is coupledout of the second partial beam 14 with the second coupler 18. The tworeference beams 13"", 14"" are superposed in a fourth coupler 71 andconducted to a second photodetector 72, which emits reference signal 70.For frequency modulation of the beam 11 of the laser 10, the modulationsignal 23 is provided, which results in a modulation of beam 11 whosetemporal characteristic corresponds to the example shown in FIG. 2.Modulator 22 need not make available any signal except modulation signal23. Without additional control signals, phase comparator 25 candetermine the phase difference from the signal 26 emitted by thephotodetector 21 and reference signal 70 emitted by the additionalphotodetector 72, and make it available at the output 27 as a measurefor the rate of rotation.

The fourth coupler 71 shown in FIG. 6 is not required for the basicfunction. It can also be omitted, in which case the two references 13"",14"" are superposed directly at the additional photodetector 72.

In all embodiments, the different optical beams can be guided completelyin optical fibers. A fifth coupler 12 that corresponds in design to thefirst and second couplers 16, 18 and the possibly provided third andfourth couplers 19, 71 is preferably provided as the means 12 forsplitting the beam 11, 50 emitted by the laser. Couplers 12, 16, 18, 19,71 preferably have respectively two coupling options on the front faces,wherein a coupling occurs as a function of the beam direction.

I claim:
 1. An optical sensor for detecting rotational movements,comprising:a laser beam source for emitting a beam; a modulator formodulating a frequency of the beam of the laser beam source; means forsplitting the beam emitted by the laser into first and second partialbeams; an annular optical fiber arrangement having a first beam pathextending in a first direction around the annular optical fiberarrangement and a second beam path extending in a second directionaround the annular optical fiber arrangement, the first direction beingopposite to the second direction, the first partial beam being coupledinto the annular optical fiber arrangement in the first direction, andthe second partial beam being coupled into the annular optical fiberarrangement in the second direction; a first beam coupler in a beam pathof the first partial beam and a beam path of the second partial beamwhich is coupled out of the annular optical fiber arrangement after thesecond partial beam has passed through the annular optical fiberarrangement; a second beam coupler in a beam path of the second partialbeam and a beam path of the first partial beam which is coupled out ofthe annular optical fiber arrangement after the first partial beam haspassed through the annular optical fiber arrangement; a photodetectorfor receiving a first coupled-out partial beam and a second coupled-outpartial beam and for generating an output signal, the first coupled-outpartial beam being derived from the first partial beam coupled out ofthe annular optical fiber arrangement, and the second coupled-outpartial beam being derived from the second partial beam coupled out ofthe annular optical fiber arrangement; an optical running period elementin the beam path of one of the first partial beam, the first coupled-outpartial beam, the second partial beam, and the second coupled-outpartial beam; and a phase comparator for determining a phase differencebetween a signal related to the modulation of the frequency of the beamof the laser beam source and the output signal of the photodetector, andfor determining a rate of rotation of the annular optical fiberarrangement based on a detected phase difference.
 2. A sensor as definedin claim 1, wherein the optical beams are guided in optical fibers.
 3. Asensor as defined in claim 1, further comprising a third coupler in thebeam paths of the first and second coupled-out partial beams forsuperposing the first and second coupled-out partial beams.
 4. A sensoras defined in claim 1, wherein the signal related to the modulation ofthe frequency of the beam of the laser beam source has a first timeinterval and the output signal of the photodetector has a second timeinterval, the first and second time intervals being substantially equalin duration.
 5. A sensor as defined in claim 1, wherein the laser beamsource is a semiconductor laser.
 6. An optical sensor for detectingrotational movements, comprising:a laser beam source for emitting abeam, the laser beam source being activated for a first predeterminedtime interval and deactivated for a second predetermined time interval;a modulator for modulating a frequency of the beam of the laser beamsource; means for splitting the beam emitted by the laser into first andsecond partial beams; an annular optical fiber arrangement having afirst beam path extending in a first direction around the annularoptical fiber arrangement and a second beam path extending in a seconddirection around the annular optical fiber arrangement, the firstdirection being opposite to the second direction, the first partial beambeing coupled into the annular optical fiber arrangement in the firstdirection, and the second partial beam being coupled into the annularoptical fiber arrangement in the second direction; a first beam couplerin a beam path of the first partial beam and a beam path of the secondpartial beam which is coupled out of the annular optical fiberarrangement after the second partial beam has passed through the annularoptical fiber arrangement; a second beam coupler in a beam path of thesecond partial beam and a beam path of the first partial beam which iscoupled out of the annular optical fiber arrangement after the firstpartial beam has passed through the annular optical fiber arrangement; aphotodetector for receiving a first coupled-out partial beam and asecond coupled-out partial beam and for generating an output signal, thefirst coupled-out partial beam being derived from the first partial beamcoupled out of the annular optical fiber arrangement, and the secondcoupled-out partial beam being derived from the second partial beamcoupled out of the annular optical fiber arrangement; an optical runningperiod element in the beam path of one of the first partial beam, thefirst coupled-out partial beam, the second partial beam, and the secondcoupled-out partial beam; an optical short-circuit between the first andsecond couplers for supplying a portion of the first partial beam to thephotodetector via the second beam coupler as a first reference beam, andfor supplying a portion of the second partial beam to the photodetectorvia the first beam coupler as a second reference beam; and a phasecomparator for determining a phase difference between a signal relatedto the modulation of the frequency of the beam of the laser beam sourceand the output signal of the photodetector, and for determining a rateof rotation of the annular optical fiber arrangement based on a detectedphase difference.
 7. A sensor as defined in claim 6, wherein the opticalbeams are guided in optical fibers.
 8. A sensor as defined in claim 6,further comprising a third coupler for superposing the first and secondcoupled-out partial beams.
 9. A sensor as defined in claim 6, whereinthe first predetermined time interval and the second predetermined timeinterval are substantially equal in duration.
 10. A sensor as defined inclaim 6, wherein the laser beam source is a semiconductor laser.
 11. Anoptical sensor for detecting rotational movements, comprising:a laserbeam source for emitting a beam; a modulator for modulating a frequencyof the beam of the laser beam source; means for splitting the beamemitted by the laser into first and second partial beams; an annularoptical fiber arrangement having a first beam path extending in a firstdirection around the annular optical fiber arrangement and a second beampath extending in a second direction around the annular optical fiberarrangement, the first direction being opposite to the second direction,the first partial beam being coupled into the annular optical fiberarrangement in the first direction, and the second partial beam beingcoupled into the annular optical fiber arrangement in the seconddirection; a first beam coupler in a beam path of the first partial beamand a beam path of the second partial beam which is coupled out of theannular optical fiber arrangement after the second partial beam haspassed through the annular optical fiber arrangement; a second beamcoupler in a beam path of the second partial beam and a beam path of thefirst partial beam which is coupled out of the annular optical fiberarrangement after the first partial beam has passed through the annularoptical fiber arrangement; a first photodetector for receiving a firstcoupled-out partial beam and a second coupled-out partial beam and forgenerating an output signal, the first coupled-out partial beam beingderived from the first partial beam coupled out of the annular opticalfiber arrangement, and the second coupled-out partial beam being derivedfrom the second partial beam coupled out of the annular optical fiberarrangement; an optical running period element in the beam path of oneof the first partial beam and the second partial beam; a referencephotodetector for receiving a portion of the first partial beam coupledout of the first coupler as a first reference beam and a portion of thesecond partial beam coupled out of the second coupler as a secondreference beam and for generating a reference signal; and a phasecomparator for determining a phase difference between the referencesignal of the reference photodetector and the output signal of the firstphotodetector, and for determining a rate of rotation of the annularoptical fiber arrangement based on a detected phase difference.
 12. Asensor as defined in claim 11, wherein the optical beams are guided inoptical fibers.
 13. A sensor as defined in claim 11, further comprisinga third coupler in the beam paths of the first and second coupled-outpartial beams for superposing the first and second coupled-out partialbeams.
 14. A sensor as defined in claim 13, further comprising a fourthcoupler in a beam path of the first reference beam and a beam path ofthe second reference beam for superposing the first reference beam andthe second reference beam.
 15. A sensor as defined in claim 12, whereinthe signal related to the modulation of the frequency of the beam of thelaser beam source has a first time interval and the reference signal andthe output signal of the reference photodetector and of the firstphotodetector, respectively, have a second time interval, the first andsecond time intervals being substantially equal in duration.
 16. Asensor as defined in claim 14, wherein the means for splitting the beamemitted by the laser into first and second partial beams comprises afifth coupler.
 17. A sensor as defined in claim 11, wherein the laserbeam source is a semiconductor laser.